Check Settings → General → Parental Restrictions and ensure that In-App Purchase is not disabled

If nothing seems to happen, wait a bit. It sometimes takes a bit to connect to the store. Also, some transactions might fail due to iTunes store outages.

If you get "In-App-Purchase Error: There was an error purchasing this item please try again." or "This is not a Test User account. Please create a new account in the Sandbox environment. [Environment Sandbox]": This may happen if you have a jailbroken iPad. Try restoring your device.

Check you are able to make purchases in other apps. If not, verify your payment settings with Apple.

Try the purchase again, you won't be charged twice

If the purchase seemed to work but doesn’t show on the list, press “Restore Purchases”. You can check on iTunes if the purchase worked.

I purchased a previous version of Conductr. I’ve reinstalled it from the store but my purchases haven’t been restored.

Make sure you have internet connection.

Make sure you are using the same purchase account that you used to purchase Conductr in the first place (iPad Configuration → iTunes and App Store → Apple ID)

Are you installing a second copy of Conductr?

Try enabling iCloud with the same account on both iPads and give it some minutes to sync (iPad Configuration → iCloud → Documents and Data, check Conductr is allowed to sync to iCloud in BOTH devices).